Is my Dell Venue Pro 'unlocked'?

Well I recently bought a DVP online on ebay and being new to the WP7 I just recently learned about the whole updating process of WP7 devices, I'm from Australia and the SIM I use works on the phone, but under the 'About' screen in settings it says my Carrier is TMO-US. Is my phone actually 'unlocked' and would I be able to receive the 7740  update if it is capable of being unlocked I am now aware that many US carriers skipped this update?